Device and method for producing a fiber composite

ABSTRACT

Method for the production of a fiber composite by placing fibers on a support, wherein long fibers are used at least as an essential component for the production of a nonwoven fabric ( 70 ). Said fibers are fed to at least one delivery head (A, A 1,  A 2 ) substantially over the height of a material column and ejected in a sustantially horizontal manner therefrom. A long fiber-air suspension is generated by adding at least one aggregate. The suspension is directly applied on the support, which is especially shaped as a molding strip ( 14 ).

This application is the national phase of international applicationPCT/DE99/00432 filed Feb. 12, 1999 which designated the U.S.

FIELD OF THE INVENTION

The invention relates to an apparatus and a method for producing anonwoven fabric from fibers.

Such nonwoven fabrics are used in particular for producingcompression-molded parts, insulating mats, and upholstery material.

PRIOR ART

Essentially two methods and corresponding apparatuses are known forproducing such nonwoven fabrics: forming a nonwoven fabric by means ofcarding/combing machines, and aerodynamic nonwoven fabric formingsystems.

The disadvantages of both systems are low or even very low throughputsand thus high costs, as well as the necessity of using at leastextensively cleaned fibers that are free of foreign bodies and have beenopened and that are therefore expensive.

Although carding/combing machines are capable of producing especiallyfine, uniform nonwoven fabrics, nevertheless they make the moststringent demands in terms of freedom from shives and the degree ofopening of the fibers. Their production output, at a maximum of 500kg/h, is very low, and the costs are correspondingly high.

If bast fibers that still contain shives are processed, for instance,they catch on the card clothings of carding/combing machines or becomedeposited in the bores of holes of the screen drums or screen belts ofaerodynamic nonwoven fabric forming systems and hinder the nonwovenfabric formation considerably, even to the extent of completeinoperability.

In the ensuing needling, hemp shives in particular deflect the needlesfrom the bores in the perforated plates onto the steel plates. As aconsequence, the needles break.

Aerodynamic nonwoven fabric forming systems make less stringent demandsin terms of freedom from shives and the degree of opening of fibers. Theoutput reaches about 1000 kg/h. This is still inadequate, however, toattain favorable costs from mass-produced products.

Cleaning the fibers of shives and opening the fibers are associated withhigh costs. Furthermore, cleaning the fibers, and especially openingthem, always leads to more or less severe mechanical damage to thefibers. This entails material losses of up to 40%. In the finalanalysis, well-cleaned and opened fibers that thus meet these demandsmade of the known systems can be created only from retted hemp or flaxstraw. Retting, however, is a biodegrading process and thus inevitablyweakens the fibers as well. For industrial purposes, fibers with maximumstrength and a maximum modulus of elasticity are required.

Other systems for forming bulk goods are used for manufacturing boardsof wood material; the final products are in particular particle boardsthat have gained extensive use in furniture making. Scattering methodsare used to produce such plates, and in these methods the chips aredelivered from a bunker to a feed roller head and from there arescattered onto a substrate by way of various intermediate processingstages. One such scattering method is described in German PatentDisclosure DE-A 4 128 592, which shows the closest prior art. However,this technique can be used only with chips that flow easily. Theflowability of the chips has the major disadvantage, however, thathardening and compacting must be done immediately after the scattering;that is, once again, additional processing stations are required toachieve an easily handled product. The aforementioned wide range of endproducts (insulating materials, molded upholstery parts,compression-molded parts) cannot be made with the chip cakes produced bythis method.

SUBJECT OF THE INVENTION

The object of the present invention is thus to produce nonwoven fabricsfor insulating purposes, upholstery materials, and the like which aredistinguished by minimal costs. In particular, the object is also toproduce nonwoven fabrics from which molded parts with a high modulus ofelasticity and high strength are created.

In a similar way, via the second nozzles 60, it is possible to apply asealing agent to the nonwoven fabric 70 as it forms, or to apply anadhesive for the sake of better adhesion of the nonwoven fabric 70 tothe first coating belt. A previously foamed material or an unfoamedmaterial with an incorporated propellant may be used as the sealingagent and binds to the surface of the nonwoven fabric 70 that is to becoated.

The fundamental concept of the invention is based on the fact thatminimal costs are attainable only if the number of production stages isreduced to a minimum and the throughput is maximized. Furthermore, thecurrently usual material losses should at least be decisively lowered.

As already mentioned above, the production stages of “separating shives”or similar substances in granulate or nodelike form that accompanyfibers, and “opening” (refinement) are extraordinarily cost-intensive.Aside from the incident operating costs, the material losses that theycause have a major effect on cost.

According to the invention, nonwoven fabrics can now be produced inwhich the two aforementioned production stages, namely “shiveseparation” and “fiber opening” are no longer needed, since with thismethod and the corresponding apparatus according to the invention, in anextreme case even uncleaned and unopened fibers can be processed. Theattendant production costs are thus dispensed with.

High fiber strength and a high modulus of elasticity are furthermoreobtainable only if retting is dispensed with. Dispensing with retting,however, means that the fibers have a much high shive content and aremuch coarser and rougher than is required for processing as in the priorart. Once again, the invention is still usable, unlike nonwoven fabricforming systems of the prior art, which cannot function at all withunretted, uncleaned and unopened fibers.

It is especially advantageous, however, that the attendant materiallosses are also avoided, which in terms of cost makes even more of adifference.

The apparatus according to the invention is furthermore capable ofproviding a yield that is multiple times greater than in prior artsystems. Costs are thus reduced to a fraction.

According to the invention, unretted, uncleaned, unopened fibers withlengths between 20 and 150 mm, preferably 30 to 70 mm, with or withoutshives and/or nonfibrous components that still stick to them and/or arelocated or scattered freely between them, with or without recycledpolymer and other fibers, can thus be formed into a single- ormulti-layer nonwoven fabric, and a throughput that is far above theprior art is attained, namely from 2000 to 9000 kg/h, preferably 2000 to4000 kg/h, for a working width of 3000 mm.

However, the method according to the invention is usable when any fibersare used, even synthetic, mineral or natural fibers, including andcleaned and opened fibers, and so forth.

Two exemplary embodiments of the apparatus of the invention will bedescribed in further detail in conjunction with drawings; shown are:

FIG. 1: a sectional view of a first preferred embodiment of theapparatus of the invention;

FIG. 2: a sectional view of a second preferred embodiment of theapparatus of the invention;

FIG. 3: a detailed view of the elements of the first and seconddischarge devices of the apparatuses of FIG. 1 or 2, and

FIG. 4: a perspective view of an exemplary embodiment of a compositeelement produced with the apparatus of the invention.

FIG. 5: a sectional view of a third preferred embodiment of theapparatus of the invention.

The exemplary embodiment shown in FIG. 1 of an apparatus for applyingfibers to a forming belt to produce a fiber composite includes anintermediate storage means in the form of a metering bunker 10, in whichthe fibers with lengths between 20 and 150 mm, hereinafter also calledlong fibers, together with optional additives, are introduced via atransverse distributor 11. The bottom of the metering bunker 10 isformed by a bottom belt 12, which moves in the direction of the arrow P1shown in FIG. 1, so that a material column M forms that is moved by themotion of the bottom belt 12 in the direction of a discharge head A. Tothis extent, the structure of the metering bunker corresponds toembodiments of the kind known from German Patent Disclosure DE-A 1 084199 or Swiss Patent Disclosure CH-A 368 301, for purposes not describedin further detail there.

A compacting belt 13 leading obliquely downward is disposed on the topside of the metering bunker 10 and moves in the direction of the arrowP2, or in other words in the same direction as the bottom belt 12. Thefeeding speeds of the transverse distributor 11, bottom belt 12, andcompacting belt 13 are adapted to one another in such a way that thematerial column M builds up between the top side of the bottom belt andthe underside of the compacting belt and is compacted by the latterbelt. The bottom belt 12 is defined on both long sides and on its backside by suitably high walls, so that the material column M, made up oflong fibers and optionally their loading materials and supplementalmaterials, assumes a substantially square or rectangular cross sectionand is thrust continuously against the discharge head A, bringing aboutthe aforementioned compacting.

The discharge head A comprises first discharge devices 20, which pointtoward the material column M, and downstream second discharge devices 30that cooperate with them and that point toward the discharge side of thedischarge head A.

The first discharge devices 20 comprise many shafts 22 (FIG. 3),preferably disposed vertically one above the other, on which laterallyspaced-apart star wheels 21 are retained, whose elements 21A pointsubstantially radially to the shaft 22 and whose front flanks 21V areembodied in hook-shaped or crescent-shaped fashion in the direction ofrotation are one.

The second discharge devices 30 also comprise shafts 32 disposedvertically one above the other, in such a way that the connecting planesE1, E2 of the shafts 22 and 32 of the two discharge devices 20 and 30are parallel to one another. Star-shaped and/or thorn-shaped elements31A are retained on the shafts 32 of the second discharge devices 30 androtate in the direction R2; the directions of rotation R1, R2 of theshafts of the first and second discharge devices are contrary to oneanother. The elements 21A and 31A are adapted to one another in terms oftheir number and shaping in such a way that their respective operativeregions mesh with one another.

On the discharge side of the thus-formed discharge head A, a suspensionchamber S is provided, whose upper boundary is formed by first nozzles40 and solids distributors 50. The nozzles 40 serve to introduce liquidloading materials into the suspension chamber S.

A forming belt 14 is guided below the suspension chamber S over asupport table 15 and is moved in the direction of the arrow P3. On thiscontinuously advancing forming belt 14, the long fibers discharged bythe discharge head A are deposited in the form of a long fiber and airsuspension, so that depending on the operating parameters of theapparatus, a nonwoven fabric 70 of adjusting thickness and consistencyforms on the forming belt.

Negative-pressure chests 16 can affect the composition and consistencyof this nonwoven fabric.

In the region below the discharge head A, second nozzles 60 areprovided, with which a sealing agent can for instance be applied to thenonwoven fabric as it forms.

In the preferred embodiment shown, above the forming belt 14, a firstcoating belt 17 is additionally guided; it serves as a carrier layer orcover layer or barrier layer of the nonwoven fabric.

First, the basic function of this apparatus will be explained:

The starting material or basic material of the nonwoven fabric 70 to beformed is placed on the transverse distributor 11; according to theinvention, this starting material contains long fibers in particular,that is, fibers with lengths preferably between 30 and 70 mm, which inturn can preferably comprise such natural fibers as hemp fibers or flaxfibers, and which are uncleaned. These long fibers can be placedexclusively on the transverse distributor 11, or they can be componentsof a mixture in which granular components, in particular such as shivesbut also polymer elements, wood granulates, and recycling foams, occur;that is, by the choice of the composition of the starting materialplaced on the transverse distributor 11, the fundamental nature of thenonwoven fabric produced in the apparatus of the invention is at leastpartly predetermined.

In particular, it is possible and desirable here for the long fibers tobe a component of a composite of natural long fibers and shives, inwhich the natural fibers and the shives are still intertwined over partof their length, or in other words are in the state in which as yet noneof the cost-intensive additional processing steps described at theoutside have been performed.

These long fibers now by themselves or together with the aforementionedmixture components form the content of the metering bunker 10 as itslowly fills, and consequently they pass to the discharge head A, whosestructure has been explained above. The described elements 21A, 31A ofthe first and second discharge devices act as milling devices, which ripor tear the long fibers or bundles of long fibers and the substances ormaterials accompanying them out of the matted material column M.

The longer the long fibers are and the more severely they are matted,the more difficult does their passage through the discharge head to theoutside become; in this decisive region, the risk of clogging increasessharply with increasing fiber length, an increasing degree of mattingand tangling, and especially with an increasing proportion of shivesthat are not completely separated from the long fibers. A particularhindrance results from the admixture of thicker and therefore stifferpolymer fibers, with the result that unless additional provisions aremade, the discharge output decreases accordingly, until the firstdischarge devices 20 are completely clogged. Consequently, the functionof the second discharge devices 30 is an especially significantsupplementation to the function of the first discharge devices 20, whichis structurally decisive for the desired goals, because the elements 31Aprovided in them accomplish the clearing, loosening and acceleration ofthe long fibers engaged by the first discharge devices 20, and thusespecially with material that mats heavily, they make the overallfunction of the discharge head A possible for the first time, byeffectively preventing clogging.

In the especially advantageous exemplary embodiment shown, the twoplanes E1, E2 (FIG. 3) of the shaft groups 22, 32 of the first andsecond discharge devices are disposed vertically; the elements of thesecond discharge devices 30 that act as clearing and acceleratingrollers, in the exemplary embodiment shown, have hooklike orcrescent-shaped ends that are oriented slightly forward and that performa plurality of functions:

First, with increased rpm, they reach between the elements 21A of thefirst discharge devices 20 and in an accelerated way rip out thematerial that is located in the discharge area and contains the longfibers. This greatly accelerates the passage of the long fiber materialthrough the rotating elements 21A, reliably prevents clogging andtangling, and thus increases the capacity of the entire system. It isself-evident that the form of the elements 21A and 31A of the twodischarge devices can be optimized to a certain extent, in terms of thelong fiber material currently being processed, by suitable shaping; manyvariants are conceivable, ranging from sharply curved, crescent-likeshapes to pinlike or thornlike shapes, especially since such variantscan also be designed structurally to be interchangeable.

Clumping of the fibers that might occur can also be completely reversedby an increased rpm of the elements 31A of the second discharge devices30; this is of particular significance for the quality of the nonwovenfabrics in terms of their strength and also the homogeneity in terms ofthe distribution of weight per unit of surface area.

The rotary speeds of the shafts 32 can be adjusted infinitely variablyin the range from 150 to 1500 rpm, for instance, so that the long fiberelements that have been ejected move in a kind of ejection parabola pathaway from the discharge side of the discharge head A. The “ejectionrange” and hence the depth of the adjoining suspension chamber S, andnaturally thus the consistency of the developing nonwoven fabric 70 aswell, can be predetermined by the choice of the rpm of the shafts 32.

For a still more-extensive definition of the “ejection paths” of longfiber elements discharged in discharge devices disposed one above theother, the individual shafts, disposed one above the other, of thesecond discharge devices 30 can be operated at a variably high rpm, forinstance with an rpm that increases toward the top, so that the longfiber material is spun only slightly away from the lower accelerationplane, while the long fiber material is spun away from the fastest,topmost roller 32 in a wide ejection parabola and rendered turbulent.Thus all the long fiber material can be pulled farther apart andloosened up to form a very loose long fiber and air suspension.

Controlling these events and thus varying the consistency and thedensity distribution of the spun-off long fiber elements are ofparticular significance for the addition of liquid loading materials, inparticular, that are to be added to the long fibers or the mixturecomponents, as will now be explained:

In contrast to short fibers of up to about 20 mm in length, the longfibers processed here cannot be acted upon by binders or other additivesbefore the nonwoven fabric formation. In the liquid state, the fiberswould become too soft and would therefore stick to the discharge devices20 and 30, so that proper nonwoven fabric formation would no longer bepossible. Dry adhesives or other additives would not even stick to longfibers in the first place. According to the invention, liquid bindersand additives are therefore not introduced, via the first nozzles 40,until after the long fiber material has emerged from the discharge headA, so that binding or admixing of such components with the long fiberelements and the mixture components optionally added to the long fiberelements beforehand takes place only immediately in the course of thenonwoven fabric formation; that is, the liquid binders, additives orfoams are sprayed or dripped into the loose long fiber and airsuspension in the desired quantitative ratio via the first nozzles 40.

This system can logically also be used for introducing solid loadingmaterials, such as additional shives, granulates or powdered binders,for which purpose solids distributors 50 are provided, which in theexemplary embodiment shown are disposed above the suspension chamber Sin alternation with the first nozzles 40.

Thus the first nozzles 40 and solids distributors 50 form a kind of“curtain” of the various desired liquid or solid loading materials intothe nonwoven fabric 70 forming on the forming belt 14, in such a waythat a largely homogeneous buildup of the nonwoven fabric 70 from thebasic materials, long fibers and loading components, is attained,regardless of whether these components are already applied to thetransverse distributor 11 in a suitable form together with the longfibers, or are expediently or necessarily applied by the nozzles 40 orthe solids distributors 50 in the event that they might excessivelyhinder the feeding of the material column M through the discharge headA.

The addition of the loading materials will therefore expediently beoptimized in this respect in such a way as to attain maximum dischargecapacities of the apparatus.

In principle, it is possible to have the nonwoven fabric 70 be built updirectly on the forming belt 14, but in the exemplary embodiment shownin FIG. 1, a first coating belt 17 is guided above the forming belt 14;depending on the choice of material, the coating belt can be selectedmerely as a substrate, or view of the later intended use of the nonwovenfabric, it can be selected from paper or plastic film with variousfunctions, such as a barrier layer.

In a similar way, via the second nozzles 60, it is possible to apply asealing agent to the nonwoven fabric 70 as it forms, or to apply anadhesive for the sake of better adhesion of the nonwoven fabric 70 tothe first coating belt. A previously foamed material or an unfoamedmaterial with an incorporated propellant may be used as the sealingagent and binds to the surface of the nonwoven fabric 70 that is to becoated.

The forming belt 14 can be used in an air-impermeable version, or (asshown) in an air-permeable version (a screen belt); in the latterembodiment, the negative-pressure chests 16 between the forming belt 14serve to smooth the severe turbulence of the long fiber material thatresults at a rotary speed of the second discharge devices 30 and toimprove the homogeneity of the material distribution over the transverseaxis of the forming belt 14.

To increase the capacity and to create an even better-optimized nonwovenfabric structure, the following provisions are possible:

The long fibers, or the long fiber and shive composites or mixtures oflong fibers with the other components in the material column M upstreamof the discharge head A have very low bulk weights, predominantlybetween 10 and 20 kg/m³, depending on the type of fiber, fiber mixture,fiber length, proportion of shives, and other components. If highthroughputs are to be attained, large structural heights of theapparatus according to the invention for the metering bunker 10 arerequired. To attain the throughput at lesser structural heights, firstthe compacting belt 13 can be used, and over its length and angle ofinclination the bulk density can be increased to a multiple of theinitial value sought, to such an extent that satisfactory operation ofthe discharge head for the long fiber composite currently involved isstill assured.

Another option for increasing the capacity and enhancing the symmetry ofthe structure of the nonwoven fabric 70, or to achieve a multi-layernonwoven fabric structure, resides in the disposition facing one anotherof two substantially structurally identical apparatuses, as shown inFIG. 2.

The basic structure and the basic mode of operation are as described forFIG. 1, so that only additional components and corresponding effectswill now be described:

In the exemplary embodiment shown in FIG. 2, the “ejection parabolas” ofthe two facing discharge heads A1, A2 for long fiber elements furnishedby metering bunkers 10A, 10B are selected so as not to overlap; that is,the result will be a two-layer nonwoven fabric 70, if the composition ofthe mixtures containing the long fibers is predetermined differently inthe two material columns M1, M2. However, it is also possible to definethe characteristic of the structure of the nonwoven fabric 70 by meansof a concentrated cooperation of the ejection speeds of the dischargedevices of the two discharge heads A1, A2 and of the effect of thenegative-pressure chests 16: The negative-pressure chests 16 can beutilized for increasing the vertical acceleration component in thesuspension chamber S, so that with the negative-pressure chests 16turned on, for instance, the form of the ejection parabolas shown inFIG. 2 results, which is relatively steep, while conversely with thenegative-pressure chests turned off and optionally with an increasedejection speed of the discharge devices of the discharge heads A1, A2, acomplete or partial overlap of the basic materials originating in thetwo bunkers can occur, so that with one and the same apparatus as shownin FIG. 2, both homogeneous, single-layer nonwoven fabrics 70 andtwo-layer nonwoven fabrics 70 can be built up on forming belt 14, whichis guided over support tables 15A, 15B, solely by controlling theaforementioned parameters.

FIG. 2 additionally shows second nozzles 60B associated with the seconddischarge head A2, for instance for applying a sealing agent to the topside of the developing nonwoven fabric, as well as a second coating belt18, which can be coated onto the top of the finished nonwoven fabric 70,for instance as a barrier layer, such as plastic film or cardboard orpaper, depending on the later intended use of the nonwoven fabric 70.

With the system described above and the method according to theinvention, nonwoven fabrics 70 with a very wide physical bolt width canthus be made, and it should be stressed very strongly that with themethod of the invention and the apparatus described, the incorporationof long fibers into such a nonwoven fabric can be masteredinexpensively, and at the same time, the physical and chemicalproperties of the resultant nonwoven fabric 70 can be defined with avery wide scope by the addition of suitable additives or loadingmaterials at a suitable point, thus offering a very wide range ofpossible uses for a nonwoven fabric of this kind. To that end, it isnaturally also possible in a known way to provide further processingstations downstream of the system of the invention, examples being acontinuous-operation band press for compacting the nonwoven fabric, or aheat treatment for action on additives, such as binders, that areincorporated into the nonwoven fabric and that are then activated inorder to enable putting the nonwoven fabric into its final state that isadapted to its intended use.

FIG. 4 briefly also shows an exemplary embodiment of one such endproduct 80; the nonwoven fabric 70 is covered on its underside by theaforementioned first coating belt 17 and on its top side and the endedges by the second coating belt 18; naturally the two coating belts 17and 18 must then be embodied so that they overlap.

Located below the nonwoven fabric 70 is an additional layer 71, whichcan for instance also be embodied as a nonwoven fabric, or as anadditionally foamed layer, for instance in a thickness range from 1 mmto 3 mm.

In summary, it can be stated that the method of the invention and theapparatuses provided for performing it make it possible for the firsttime economically to incorporate long fibers, and in particularuncleaned natural fibers, into a wide range of industrially useful endproducts, such as insulation mats, profiled parts, and also moldedparts, which must have a high intrinsic rigidity, in each case by theaddition of suitable additives. With the use especially of natural longfibers in the uncleaned state, a previously impossible but highlydesirable combination of ecology and economy in this field is nowfeasible, which makes the specific advantages of such natural materialsaccessible to a wide range of industrial uses.

With the method described and the apparatus intended for performing it,however, it is readily possible in an extension of the concept of theinvention to produce multi-layer nonwoven fabrics without having to usea plurality of nonwoven fabric forming machines, each of which makes oneply or layer, as is required in the prior art:

Multi-layer nonwoven fabrics, especially in the automotive field, offerthe possibility of producing molded parts for inner linings of naturalfibers as well; the surface is sealed in vapor-proof fashion while beingpressed, for instance to avoid the development of condensate, moistureand mold at critical points in the region of the natural fibers. Thiscan be done by applying a film lining to the outside, for instance bythe aforementioned combination of the nonwoven fabric with the coatingbelt 17 or 18. In the refinement described below, however, it is alsopossible to produce the cover layers of the nonwoven fabrics, forinstance, from pure polymer fibers and to incorporate a high proportionof natural fibers only into the main layer in the middle. In the ensuingpressing operation, by suitably regulating the temperature and pressure,it can be assured that the outer layers, which comprise polymer fibers,will melt completely and in the pressing operation will then form acontinuous or vapor-proof polymer skin on one or both sides. Comparedwith the application of a polymer film lining, such as the coating belt17 and 18, this version has the advantage that the polymer fibers, asthe three-layer nonwoven fabric is laid, will partly intersect or becomematted with the natural fibers of the middle layer and as a result, amuch more solid connection between the layers is formed than when apolymer film is applied as a lining on the outside. Molded partsproduced in this way are capable of withstanding heavier loads thanlined molded parts and thus increase the safety of passengers in theevent of a crash.

For producing insulating material as well, a two- or three-layeredstructure of a nonwoven fabric can be advantageous, because polymerfibers combine with one another to form a solid layer more easily thando natural fibers. By making both cover layers of an insulating nonwovenfabric from polymer fibers, for instance, but making the actualinsulating layer that represents the main cross section from 90% naturalfibers, for instance, with only 10% polymer fibers acting as supportingand binding fibers, and by then passing this fiber composite through athermal furnace, a nonwoven fabric is obtained that has twohigh-strength cover layers that are strongly fused by thermobonding,which hold the looser core of the natural fiber and polymer fibermixture together like a skin and enable a simple incorporation.

FIG. 5 shows a sectional view through a third preferred embodiment ofthe apparatus of the invention, with which the described multi-layerstructure of a fiber composite is possible without major effort orexpense:

Instead of the single transverse distributor 11 (see FIG. 1), in thisexemplary embodiment for producing a three-layer fiber composite, threetransverse distributors 11A, 11B, 11C are correspondingly disposed inthe metering bunker; their horizontal and vertical positioning and theirfeeding speed determine the relative thickness of the layers that arefinally formed in the fiber composite. Each of these transversedistributors 11A, 11B, 11C serves to deliver one component of themulti-layer nonwoven fabric; in the last exemplary embodiment mentioned,for producing an insulating material, the transverse distributors 11Aand 11C would consequently supply polymer fibers, while the transversedistributor 11B would supply a mixture of 90% long fibers and 10%polymer fibers.

Instead of the single material column M in the buildup of a homogeneousfiber layer as in FIG. 1, consequently three material layers MA, MB, MCform, one above the other, each in the applicable fiber composition.These material layers are delivered from the bottom belt 12 continuouslyto the discharge head A with its discharge devices 20 and 30 and areejected by them to form the multilayer nonwoven fabric. The rotationalspeed of the discharge devices can be determined such that the “ejectionparabolas” or individual fiber components of the various material layersextend in such a way that upon arrival on the forming belt, either acertain mixing of adjacent material layers or a sharp distinctionbetween such material layers can be established selectively. Thesharpness of the distinction between individual material layers 70A,70B, 70C can also be further regulated by the speed and course of theair, with the aid of the negative-pressure chests 16.

For example, the upper discharge device can be adjusted to a higher rpmand the lower discharge device to a lower rpm than the rpm of the middledischarge devices, resulting in a wide spread via the ejection parabolasof the particles of the individual material layers, so that during theejection, no overlap of ejection paths occurs, and thus a relativelysharp separation between the layers on the multi-layer nonwoven fabricis also attained.

Conversely, if diffuse boundaries between individual material layers inthe multi-layer nonwoven fabric are desired, then the negative-pressurechests should be shut off, and the discharge devices should becontrolled in terms of their rpm in opposite directions, so that on theone hand a longer float time is achieved, while on the other theejection parabolas of the particles of the material layers, stacked oneabove the other, mix until their arrival on the forming belt, so thatover the complete thickness of the resultant multiple nonwoven fabric, acontinuous transition of material between the individual layers can beachieved.

Even in this kind of design, a selective imposition of the loadingmaterial on the natural fiber component (that is, the middle materiallayer in this exemplary embodiment) can also be achieved by a modifiedarrangement of the solids distributors 50 and nozzles 60.

The thus-formed nonwoven fabric can then be solidified by thermobonding,needling or the like, to enable its handling in the ensuing processingoperations.

The apparatus according to the invention, in the third exemplaryembodiment described, thus makes it possible, without major investment,to create a multi-layer fiber composite for producing a nonwoven fabric,in which the components and their transitions at the boundary layers canbe selected or adjusted in a simple way by means of control parametersthat are available anyway.

Especially in the last exemplary embodiment described above, it is evenpossible to dispense completely, or from time to time, with the additionof loading materials, for specific nonwoven fabric embodiments.

What is claimed is:
 1. A method for producing a fiber compositecontaining fibers that constitute at least an essential component of thecomposite, the fibers having lengths between 20 and 150 mm and beingdelivered substantially above the height of a material column to a firstdischarge device through which the fibers are pulled out of the materialcolumn and then to a second discharge device which, for the productionof a nonwoven fabric with the fibers, directly cooperates with the firstdischarge device for loosening, clearing and accelerating fibers pulledout of the first discharge device by imparting to the fibers asubstantially horizontal acceleration, resulting in ejection of thefibers along parabolic trajectories with an adjustable ejection rangeestablished by adjusting operating parameters of the second dischargedevice, to thereby place and distribute the fibers on a forming belt. 2.The method of claim 1, in which at least one loading material is addedto the fibers, characterized in that the loading material is added in asuspension space (S) of a fiber and air suspension, which space isformed between the second discharge device and the forming belt.
 3. Themethod of claim 1, in which at least one loading material is added tothe fibers, characterized in that the fibers are a component of amixture in which binders, granulates or granular components occur as theloading material.
 4. The method of claim 3, characterized in that themixture comprises uncleaned natural fibers.
 5. The method of claim 4wherein the uncleaned natural fibers comprise hemp fibers, oiled linenfibers, flax fibers or fibers of jute, kenaf, sisal, or mixturesthereof.
 6. The method of claim 3 in which the loading material includesshives, polymer parts, wood granulates, recycling foams.
 7. The methodof claim 1, characterized in that the fibers are compacted during theirfeeding to the first discharge device.
 8. The method of claim 1,characterized in that the nonwoven fabric has two surfaces and at leastone sealing agent for at least one of the two surfaces of the nonwovenfabric is added via the forming belt.
 9. The method of claim 8,characterized in that a previously foamed material or an unfoamedmaterial with an incorporated propellant is used as the sealing agentand binds to the surface of the nonwoven fabric that is to be coated,and optionally binds a cover layer or barrier layer to the nonwovenfabric.
 10. An apparatus for performing the method of claim 1, having ametering bunker for the material column and having a plurality of first,vertically staggered discharge devices for engaging the fibers from thefront of the material column and metering them, and having a formingbelt guided below the first discharge devices, characterized in that thefirst discharge devices are disposed substantially vertically one abovethe other, and that a plurality of second discharge devices areprovided, which are used for clearing, loosening and accelerating thefibers.
 11. The apparatus of claim 10, characterized in that: theapparatus further comprises a transverse distributor for delivering thefibers to the metering bunker; the metering bunker has a bottomvia whichthe fibers are supplied to the first discharge devices; and theapparatus further comprises a compacting belt which extends obliquelydownward between the transverse distributor and an upper end of thefirst discharge devices and that acts upon the material column thatcontains the fibers.
 12. The apparatus of claim 10, characterized inthat the first discharge devices comprise star wheels that are heldspaced apart on a shaft, the star wheels having elements that pointsubstantially radially to the shaft and front flanks that are orientedin a direction of rotation of the star wheels; that the second dischargedevices have elements disposed in at least one of a starlike andthornlike form on a shaft for clearing, loosening and acceleration ofthe fibers; and that operative regions of the elements of the first andsecond discharge devices at least partly overlap or mesh with oneanother.
 13. The method of claim 12 wherein the front flanks of the starwheels have a hooklike or crescent-shaped form.
 14. The apparatus ofclaim 10, characterized in that first nozzles for introducing liquidloading materials into the fiber and air suspension are disposed above adischarge side of at least one of the discharge devices.
 15. The methodof claim 14 wherein the liquid loading materials comprise binder orflame retardant.
 16. The apparatus of claim 10, characterized in thatsolids distributors for introducing solid loading materials into thefiber and air suspension are disposed above a discharge side of at leastone of the discharge devices.
 17. The method of claim 16 wherein thesolid loading materials comprise shives, granulates or powdered binders.18. The apparatus of claim 10, characterized in that the apparatusfurther comprises devices for introducing sealing agent, the devicescomprising two nozzles disposed in a region below at least one of thedischarge devices.
 19. The apparatus of claim 10, characterized in thata first coating belt as a substrate/cover layer/barrier layer of thenonwoven fabric is guided on the forming belt.
 20. The apparatus ofclaim 19, characterized in that the first coating belt is wider than thenonwoven fabric.
 21. A method for producing a multi-layer fibercomposite of claim 1, characterized in that the material columncomprises at least two material layers located one above the other,which are simultaneously delivered to the discharge devices.
 22. Themethod of claim 21, characterized by the use of polymer fibers in thematerial layers.
 23. The method of claim 22, characterized in that thematerial layers include uppermost and lowermost material layers composedexclusively of polymer fibers.